As a device for detecting transformation, such as flexure, of a detection object, there has hitherto been one using a piezoelectric substance in Patent Document 1. In this device, a detection electrode is formed on a flat membrane type piezoelectric substance, to configure a flat membrane type piezoelectric sensor. This piezoelectric sensor is stuck to a detection object portion such as an elbow. A voltage outputted from the piezoelectric sensor is detected in accordance with bending of the detection object portion (elbow).
The piezoelectric substance used in such a piezoelectric sensor generates a voltage in accordance with an amount of bending at the moment of application of bending stress.
Patent Document 1: Unexamined Japanese Patent Publication No. 2006-038710
However, in the piezoelectric substance, when a bending state is held constant, charge is attenuated and the voltage turns back to an original state. For example, assuming that a voltage value in a first state as a reference state is Vs[V]. Even when bending stress is applied and a voltage value of ΔV12[V] is generated in a second state, if the second state is held, the voltage value turns back to the voltage value of Vs[V] for the first state. That is, when time elapses while the piezoelectric substance is in the second state where the piezoelectric substance has been bent just in a predetermined amount of bending, the piezoelectric substance is detected with the voltage value Vs[V] for the first state.
When the piezoelectric substance is further displaced into a third state while such a state as above is held, a voltage value of ΔV23[V] is generated, the voltage value corresponding to an amount of displacement from the second state to the third state. However, in this case, a voltage value to be a reference at the time of detecting the third state is Vs[V]. Therefore, the voltage value at the timing of detecting the third state is Vs+ΔV23 [V].
Here, the third state has occurred from the first state via the second state, and the voltage value should normally be Vs+ΔV12+ΔV23 [V].
Hence the detected voltage value does not agree with the actual amount of displacement.